Isolation and amino acid sequence of COOH-terminal fragments from the beta subunit of human choriogonadotropin.

S Birken,R E Canfield

doi:10.1016/s0021-9258(19)63360-0

Abstract

The amino acid sequence of the unique COOH-terminal region of the beta subunit of human choriogonadotropin has been reinvestigated. The desialylated subunit was digested with thermolysin and a 27-residue peptide from positions 115 through 141 isolated in a high yield. Quantitative Edman sequence degradation of this peptide, of another peptide produced by thermolysin digestion containing residues 142 to 145, and of two tryptic peptides (residues 123 to 145, 134 to 145) has established that the amino acid sequence of this region is: (formula: see text). In addition, the positions of attachment of the carbohydrate moieties to serine residues was established by a direct procedure using alkaline elimination and 35S-labeled sulfite addition, which yields [35S]-cysteic acid residues at the site of a substituted serine. Carbohydrate side chains in the COOH-terminal region have been shown to exist at residues 121, 127, 132, and 138. These studies have also resulted in the development of improved methods for the purification of COOH-terminal peptides of the human choriogonadotropin beta subunit.

Highlights

The positions of attachment of the carbohydrate moieties to serine residues was established by a direct procedure using alkaline elimination and 35S-labeled sulfite addition, which yields [%I
Since synthetic peptides containing this unique sequence of the hCG p subunit provide the most promising source of antigens to raise antibodies that distinguish hCG from hLH, it is important to resolve these disagreements about the primary structure
Column A gives the analysis obtained for the peptides as isolated, while column B is the analysis obtained after the alkaline p elimination, converting substituted serine residues to cysteic acid. - = co.05 residue

Summary

PROCEDURES

Hormone Preparation - Crude human choriogonadotropin was purchased from Organon (Oss, Netherlands) and purified as described earlier [15]. Human choriogonadotropin (hCG) is a glycoprotein hormone synthesized by trophoblast cells early in pregnancy [1, 2]. Subunits of this hormone [3, 4] have revealed a high degree of homology with the Antibodies that bind hCG and do not bind hLH have been used as tumor markers and to make the diagnosis of pregnancy as early as several days following fertilization

RESULTS

TABLE I

Composite sequence

EDMAN CYCLE NUMBER

DISCUSSION